This invention relates to microelectromechanical systems (MEMS), and more specifically to MEMS actuators.
Microelectromechanical systems (MEMS) have been developed as alternatives to conventional electromechanical devices, such as relays, actuators, valves and sensors. MEMS devices are potentially low-cost devices, due to the use of microelectronic fabrication techniques. New functionality also may be provided, because MEMS devices can be much smaller than conventional electromechanical devices.
Many applications of MEMS technology use actuators that include one or more beams that are actuated electrostatically, magnetically, thermally and/or using other forms of energy. Examples of MEMS actuators using thermal arched beam structures are described in U.S. Pat. No. 5,909,078 to Wood et. al., the disclosure of which is hereby incorporated herein by reference. Among the arched beam structures described therein are structures including one or more arched beams that extend between spaced apart supports on a microelectronic substrate and which expand and contract in response to heating and cooling, thereby causing displacement of the arched beam.
Such thermal arched beam structures can be used to provide actuators, relays, sensors, microvalves and other MEMS devices. Examples of thermal arched beam microelectromechanical devices and associated fabrication methods also are described in U.S. Pat. No. 5,955,817 to Dhuler et al. entitled Thermal Arched Beam Microelectromechanical Switching Array; U.S. Pat. No. 5,962,949 to Dhuler et al. entitled Microelectromechanical Positioning Apparatus; U.S. Pat. No. 5,994,816 to Dhuler et al. entitled Thermal Arched Beam Microelectromechanical Devices and Associated Fabrication Methods; U.S. Pat. No. 6,023,121 to Dhuler et al. entitled Thermal Arched Beam Microelectromechanical Structure; and U.S. patent application Ser. No. 09/275,058 to Edward A. Hill, filed Mar. 23, 1999, the disclosures of all of which are hereby incorporated herein by reference in their entirety.
Developments in MEMS technology have led to actuators that offer desirable displacement and force capabilities. However, the displacement, force and/or reliability of such devices may be limited by materials and structural configuration. For example, stress generated in an arched beam actuator may limit the range of displacement and/or force over which the beam may be operated without causing permanent deformation or failure. Performance of MEMS actuators may also be limited by stability considerations. Accordingly, there is an ongoing need for MEMS actuators that may provide increased stability and reliability in comparison to conventional designs.
According to embodiments of the present invention, a microelectromechanical actuator includes a substrate. A beam has respective first and second ends attached to the substrate and a body disposed between the first and second ends having a sinuous shape. The body includes a portion operative to engage a object of actuation and apply a force thereto in a direction perpendicular to the beam responsive to at least one of a compressive force and a tensile force on the beam. The sinuous shape may be sinusoidal. For example, the sinuous shape may approximate a single period of a cosine curve or a single period of a sine curve. The first and second ends of the beam may be both fixedly attached to the substrate, or at least one of the first and second ends may be attached to the substrate by at least one movable support, such as an actuator beam. According to other embodiments of the present invention, the sinuous shape approximates a bending mode shape of a straight beam. The beam shape may represent, for example, a continuous or piecewise approximation of the bending mode shape.
According to yet other embodiments of the invention, a microelectromechanical actuator includes a substrate and a beam having respective first and second ends attached to the substrate and a body disposed between the first and second ends. The body includes a portion operative to engage a object of actuation and apply a force thereto in a direction perpendicular to the beam responsive to at least one of a compressive force and a tensile force on the beam. The beam is configured such that the body assumes a sinuous shape if freed from the substrate. The sinuous shape may be sinusoidal, e.g., the sinuous shape may be a continuous or piecewise approximation of a sinusoidal curve or of a bending mode of a straight beam.
According to still other embodiments of the present invention, a microelectromechanical rotary actuator includes a beam having first and second ends attached to a substrate and a body disposed between the first and second ends. The body includes first and second oppositely inflected portions meeting at a point between the first and second ends. The body is operative to engage an object of actuation and rotate the object of actuation around the point at which the oppositely inflected portions meet responsive to at least one of a compressive force and a tensile force on the beam. The first and second oppositely inflected portions may be curved. For example, the body may have a sinusoidal shape approximating a period of a sine curve.
In other embodiments of the present invention, a rotary actuator includes first and second beams, a respective one of which has first and second ends attached to a substrate and a body disposed between the first and second ends. Each body includes first and second oppositely inflected portions meeting at a point between the first and second ends. The bodies of the first and second beams intersect one another at the points at which the first and second oppositely inflected portions of the first and second bodies meet. The bodies of the first and second beams are operative to engage the object of actuation and rotate the object of actuation around the point at which the first and second bodies intersect responsive to at least one of compressive force and tensile force on the first and second beams.
According to other embodiments of the present invention, a microstructure comprises a substrate and a sacrificial layer on the substrate. A beam having respective first and second ends attached to the substrate and a sinusoidal body is disposed between the first and second ends and on the sacrificial layer. The sinusoidal body may have, for example, a shape approximating a period of a cosine curve or a period of a sine curve.
In yet other embodiments of the present invention, a microstructure includes a substrate and a sacrificial layer on the substrate. A beam has respective first and second ends attached to the substrate and a body disposed between the first and second ends and on the sacrificial layer. The body has a shape approximating a bending mode shape of a straight beam. The shape of the body may be a substantially continuous or piecewise approximation of the bending mode shape.
According to method aspects of the present invention, a microstructure is fabricated by forming a sacrificial layer on a substrate and forming a beam having respective first and second ends attached to the substrate and a sinusoidal body disposed between the first and second ends and on the sacrificial layer. At least a portion of the sacrificial layer is removed to release the sinusoidal body. The sinusoidal body may, for example, have a shape approximating a period of a cosine curve or a period of a sine curve.
According to yet other method aspects, a microstructure is fabricated by forming a sacrificial layer on a substrate and forming a beam having respective first and second ends attached to the substrate and a body disposed between the first and second ends and disposed on the sacrificial layer, the body having a shape approximating a bending mode shape. The shape of the body may be a substantially continuous or piecewise approximation of the bending mode shape.
According to still other method aspects of the present invention, an object of actuation is rotated by engaging the object of actuation with a beam having first and second ends attached to a substrate and a body disposed between the first and second ends, the body including first and second oppositely inflected portions meeting at a point between the first and second ends. One of a compressive force or a tensile force is applied to the beam to rotate the object of actuation around the point at which the oppositely inflected portions meet. The body of the beam may have a sinusoidal shape, e.g., the body shape may approximate a period of a sine curve or a second bending mode shape of a straight beam. The object of actuation may be engaged with first and second beams, a respective one of which has first and second ends attached to the substrate and a body disposed between the first and second ends, each body including first and second oppositely inflected portions meeting at a point between the first and second ends, wherein the bodies of the first and second beams intersect one another at the points at which the first and second oppositely inflected portions of the first and second bodies meet. Respective compressive or tensile forces may be applied to the first and second beams to rotate the object of actuation around the point at which the first and second bodies intersect.